On rotating machines, it is often necessary to detect the torques thereof during the operation. For that, especially torques of rotating shafts are measured, of which the torque transducers rotate synchronously with the shaft and permanently detect the torque or rotational moment transmitted through the shaft. For this, often torque sensors equipped with torque measuring strips or torque gages are utilized, which are positioned between the rotating shaft parts and are fastened thereon. For that, the torque transducers usually have ring-shaped or annular fastening flanges, which are screwed or bolted together with oppositely lying flanges of the shafts. In that regard it is often necessary that the torque transducers are also fastened in relatively short shaft pieces or between existing available flanges, whereby only little axial structural space is available. In that regard, such fastenings must be carried out such that as little as possible interfering stresses or interfering forces can get into the strain measuring body or deformation body, in order to ensure a high measuring accuracy.
A very short structurally assembled torque sensor is known from the DE 42 08 522 C2, which is embodied with a disc shape. This one-piece torque transducer consists of an outer ring and an inner hub concentric thereto, which are connected with one another through four radially extending measuring webs. In that regard, the measuring webs comprise axial opposite-lying pocket-shaped recesses, through which a thin-walled end face remains at the base of the pocket, onto which shear force transducers in the form of foil strain gages are applied. In that regard, the shear force transducers detect the transmitted torque on the strain measuring bodies on the base of the pockets. For introducing (or inputting) and leading out (or outputting) the torque that is to be transmitted, preferably eight bores are introduced both into the inner hub as well as into the outer ring, onto which bores the shaft ends are securely screwed. Because the fastening bores of the inner hub are arranged relatively close to the measuring webs, interfering bending stresses or other parasitic forces can have an influence on the measuring webs due to different screwing connections and production tolerances, and these interfering bending stresses or other parasitic forces then falsify the measuring result.
A torque sensor in which the fastening areas are located relatively far away from the strain measuring body is known from the EP 1 074 826 B1. This torque sensor is embodied in a one-piece manner and includes two axially opposite-lying fastening flanges, which are connected with one another by a short axial torque transmission element at a radially inwardly lying area. The torque transmission element consists of an inwardly closed cylindrical circumferential surface and radially outwardly directed axial webs, between which measuring pockets are arranged coaxially to the rotation axis. Through the measuring pockets there arise thin membrane-like strain areas as deformation bodies, on which strain gages are applied, which supply an exact measuring signal, which is proportional to the transmitted torque. Because the two fastening flanges comprise an equally large diameter and the fastening bores are arranged on the outer ring surfaces thereof, it is ensured that interfering bending stresses or other parasitic forces are hardly effective or active in the strain measuring bodies lying symmetrically therebetween, whereby the strain measuring bodies have the strain gages. However, the pipe-shaped measuring body is arranged in the longitudinal direction between the two fastening flanges, so that such a torque sensor is structurally too long for many applications and therefore is not utilizable in short shaft areas.
From the DE 44 30 503 C1, there is known a longitudinally very short torque sensor, which similarly comprises two equally sized rotationally symmetrical fastening flanges. These are arranged parallel and lying axially opposite, are embodied disc-shaped, and are welded together with one another radially inwardly through a massive ring-shaped force transmission part. Thereby, the two fastening flanges are spaced axially from one another by only a small air gap. In that regard, one of the two fastening flanges is equipped with a strain measuring body encircling around coaxially to the rotation axis, on the ring-shaped outer end face of which strain gages in the form of shear force transducers are applied. In that regard, the strain measuring body is formed by two axially opposite, coaxially encircling annular or ring grooves, which are machined out of the fastening flange embodied as a measuring flange. The strain measuring body remaining between the ring grooves is thereby arranged radially between the ring-shaped outer fastening part and the inwardly lying force transmission part. Due to the radially diminishing tangential force effect, the circular ring-shaped strain measuring body part is embodied with a uniformly diminishing thickness from the inside toward the outside. Because the entire torque must be transmitted via the circular ring-shaped measuring body part, its axial thickness is dimensioned relatively large, whereby the measuring sensitivity is reduced. Simultaneously, interfering bending stresses or other parasitic forces are also transmitted via the uniform circular ring-shaped embodied measuring body part, whereby the measuring accuracy can additionally be impaired.